Regulation of 11 β-hydroxysteroid dehydrogenase type 2 by steroid hormones and epidermal growth factor in the Ishikawa human endometrial cell line

Abstract

The biological actions of glucocorticoids in target organs are determined at least in part by the local expression of 11 β-hydroxysteroid dehydrogenase type 2 (11 β-HSD2), which is responsible for the inactivation of glucocorticoids. The human endometrium is a glucocorticoid target tissue, and is known to express 11 β-HSD2. However, little is known about the function and regulation of 11 β-HSD2 in the endometrium, probably owing to the lack of in vitro model systems (i.e., cell lines) that express 11 β-HSD2. Here, we describe the characterization of 11 β-HSD expression in Ishikawa cells, a well-differentiated human endometrial adenocarcinoma cell line. The 11 β-HSD activity in intact Ishikawa cells was characteristic of 11 β-HSD2 in that it only possessed dehydrogenase activity (cortisol to cortisone) and had a high affinity for cortisol (apparent K m of 34 nM). The exclusive expression of 11 β-HSD2 in Ishikawa cells was confirmed by RT-PCR which demonstrated the presence of the mRNA for 11 β-HSD2 but not that for 11 β-HSD1. To investigate the regulation of 11 β-HSD2 in Ishikawa cells, we treated these cells with sex steroid hormones, glucocorticoids and epidermal growth factor (EGF), and determined the effects of these treatments on 11 β-HSD2 activity by an established intact cell radiometric conversion assay. Treatment with estradiol-17 β (E 2, 10 nM) and medroxyprogesterone acetate (MPA, 100 nM) produced a classic sex steroid effect; the greatest increase (330% of the control) in the level of 11 β-HSD2 activity was caused by the combined treatment, followed by MPA (240% of the control) with E 2 being the least effective (156% of the control). The stimulatory effect of E 2 was blocked by the pure antiestrogen ICI 182,780. The synthetic glucocorticoid dexamethasone (Dex) increased 11 β-HSD2 activity in a time- and dose-dependent manner (200% of the control; 100 nM for 48 h), and the endogenous glucocorticoid cortisol was equally effective in this regard. The antiprogesterone-antiglucocorticoid RU486 did not counteract with MPA or Dex but rather acted as an agonist; increased 11 β-HSD2 activity (160% of the control; 100 nM for 72 h). By contrast, treatment with EGF caused a dose- and time-dependent decrease in 11 β-HSD2 activity (60% of the control; 10 ng/ml for 72 h). In addition, semi-quantitative RT-PCR analysis revealed that there were corresponding changes in the level of 11 β-HSD2 mRNA following the treatment of Ishikawa cells with these steroid hormones and EGF, indicating that the effects of these hormones and EGF are mediated, at least in part, at the level of 11 β-HSD2 gene transcription. In conclusion, we have demonstrated for the first time that the human Ishikawa endometrial cell line expresses exclusively the 11 β-HSD2 isozyme. Moreover, we have presented the first direct evidence that sex steroid hormones and glucocorticoids stimulate while EGF inhibit the expression of 11 β-HSD2 in Ishikawa cells, suggesting that endometrial 11 β-HSD2 is under the control of steroid hormones and EGF. Thus, the Ishikawa cell line represents an excellent model in which the function and regulation of endometrial 11 β-HSD2 may be studied.